98 



MINERALS AND GEOLOGY 



(4 9 per cent.), alumina (30 44 per cent.), with more or less 

 quioxide of iron, magnesia, protoxide of iron, protoxide of manganese, 

 lime (under 2 per cent.), soda, potash and sometimes lithia. A small 

 amount of fluorine is also generally present. 



Tourmaline is of comparatively common occurrence in the Lauren- 

 tian strata of Canada. It is met with both in the crystalline lime- 

 stones and in many of the gneissoid or quartz beds of that formation, 

 as well as in some of the granitic veins by which these beds are 

 traversed. In the Ottawa district, it occurs especially in crystalline 

 limestones, as at Calumet Falls (yellowish-brown and black, with 

 Idocrase, <fcc.) ; in Clarendon Township, County of Pontiac ; in 

 North Burgess and Elmsley, Lanark County ; in Grenville, and at 

 Lachute, in Argenteuil County and elsewhere. In Ross, Elmsley, 

 Bathurst, Ely thtield (near the High Falls of the Madawaska), St. 

 Jerome (Terrebonne County), Gal way (Peterborough County), and 

 on Yeo's Island, Stoney Lake, Charleston Lake, &c., it is found in 

 granitic and syenitic veins. Also in quartz veins and beds associ- 

 ated with gneissoid strata, in various parts of Madoc, Tudor, Elzevir, 

 and more or less generally throughout the back country between the 

 Ottawa and Georgian Bay. 



47. Garnet: Variously coloured most commonly red, brown, 

 black, green or yellow : rarely colourless. Regular in crystalliza- 

 tion : the crystals almost invariably either rhombic dodecahedrons 

 or trapezohedrons (Figs. 59 and 60). The mineral occurs also, very 

 commonly, in granular and lamellar 

 masses. H 6.5 7.0 ; sp. gr. 3.5 

 4.2. BB, most varieties melt more 

 or less readily, the dark-red yielding 

 a magnetic globule ; but the bright- 

 green chrome garnet and some light- FW. 59. FIG. eo. 

 coloured varieties are infusible. After fusion or strong ignition, 

 most varieties gelatinize in boiling hydrochloric acid (see under 

 " Action of Acids," Part I.). Composition exceedingly variable, but 

 essentially silica (33 to 43 percent.), alumina or sesqui-oxide of iron 

 (or both), with either lime, magnesia, protoxide of iron, or protoxide 

 of manganese, or several of these bases combined. In the bright- 

 green garnet (Ouvarovite), the sesquioxide of iron is chiefly re- 

 placed by sesquioxide of chromium, *and the monoxidized portion of 



